1. Field of the Invention
The present invention relates to elevator systems. In particular, the present invention provides a method and apparatus for isolating elevator cars and platforms from vibrations.
2. Description of the Related Art
Vibrations are typically induced in elevator systems by a variety of sources. As elevator cars traverse elevator shafts, vibrations are induced by curves in the guide rails and by level differences in the guide rails. Moreover, an elevator hoist rope can transmit elevator lift motor vibrations to an elevator car. In addition, aerodynamic forces, braking forces and other mechanical sources induce a range of vibrations in an elevator system and these vibrations are often transmitted to an elevator car operating in the elevator system. In a modern elevator system, an elevator car sits on a platform that is mounted to an elevator sling. The platform is suspended from the sling by steel cables or brace rods. These cables or brace rods transmit the vibrations from the elevator system to the elevator platform and elevator car. The average power transmitted by these rods and/or cables is a function of their density, which, in the case of steel, is relatively high.
To prevent transmission of vibrational energy from the elevator system to the elevator car, most elevator manufacturers employ isolation devices, such as isolation pads, primarily manufactured from rubber, between the cables or brace rods and the elevator platform. In some applications, the platform may rest on a rubber pad that in turn rests on the elevator sling. While rubber isolation pads are relatively inexpensive and provide some attenuation to vibrations that occur in elevator systems, they have a relatively high natural frequency. Under standard loading conditions, rubber isolation pads and rod braces have a natural frequency of about 20 Hz. Attenuating media can only attenuate vibrations whose frequencies are greater than about 1.141 times the natural frequency of the attenuating media. Thus, rubber isolation devices can only attenuate vibrations over a relatively limited range of frequencies.
The present invention provides a vibration attenuated elevator car assembly and method for isolating an elevator car from vibrations having a range of frequencies that are typically encountered in elevator systems. According to one embodiment of the present invention, a vibration attenuated elevator car assembly for attenuating elevator system vibrations is used to secure an elevator car platform to an elevator sling that travels on elevator rails in an elevator shaft. The vibration attenuated elevator car assembly comprises an elevator car platform that is horizontally suspended from the elevator sling by upper tension members and that is also secured to a lower portion of the elevator sling by lower tension members. Thus, the elevator car platform is not indirect contact with the elevator sling.
Preferably, the elevator car is isolated from elevator system vibrations by suspending the elevator car platform from an upper portion of the elevator sling with tension members manufactured from synthetic fiber because synthetic fibers transmit significantly less energy at any tension, frequency, and amplitude than steel due to their lower density. Material containing aramid fibers, such as Kevlar(copyright) rope or Kevlar(copyright) cored rope with a Nomex(copyright) sheath, is particularly well-suited for use as a tension member because it has relatively low in-use natural frequencies. Vectran(copyright) and generic Aramid are also well-suited for use with the present invention.
As an alternative to using lower tension members, the elevator car platform may be secured to a safety plank or other lower structural member of the elevator sling with isolation mounts. In this embodiment, the car platform would still be suspended from the sling with upper tension members having an in-use natural frequency below that of the vibrations typically found in the elevator system.